Formic acid regulated lanthanum-based metal organic framework material adsorbent as well as preparation method and application thereof

Abstract

The invention discloses a formic acid regulated lanthanum-based metal organic framework material adsorbent as well as a preparation method and application thereof, and belongs to the technical field of adsorption of phosphate in water. The preparation method of the lanthanum-based metal organic framework material adsorbent comprises the following steps: mixing lanthanum salt, terephthalic acid, formic acid and a solvent, and performing solvothermal reaction to obtain the lanthanum-based metal organic framework material adsorbent. According to the invention, the formic acid is adopted to adjust the preparation of the lanthanum-based metal organic framework material, so that the phenomena that the traditional La-MOFs material is small in specific surface area and easy to agglomerate are changed, and the adsorption performance of the material on phosphate is further enhanced; the problem that an existing La-MOFs material is low in phosphate adsorption performance is solved.

Description

Technical Field

[0001] The invention relates to the technical field of phosphate adsorption in water, and in particular to a formic acid-regulated lanthanum-based metal organic framework material adsorbent and a preparation method and application thereof. Background Art

[0002] Phosphorus is a basic element for the survival of organisms and plays an important role in the cellular metabolism of organisms. However, when the phosphorus content in water is too high, it will lead to eutrophication, which in turn will lead to problems such as reduced biodiversity, homogenized community structure, and unstable ecosystems. Therefore, the research on efficient phosphorus removal technology is imminent. At present, the main methods for phosphorus removal are chemical precipitation, crystallization, biological treatment, electrolysis, and adsorption. Among them, the adsorption method has attracted widespread attention due to its simple process, convenient management, and low installation and maintenance costs of treatment equipment. What is particularly important is that the adsorption performance of the adsorbent, as the core element for evaluating its effectiveness, is not only directly related to the quality of the adsorption effect, but also a key bridge connecting the efficient operation of the adsorption technology with the realization of ecological environmental protection goals.

[0003] Metal-organic frameworks (MOFs) are widely used in gas storage, catalysis, adsorption and other fields due to their large specific surface area, adjustable pore size and simple preparation method. The adsorption performance of traditional lanthanum-based metal-organic frameworks (La-MOFs) adsorbents for phosphate needs to be improved. Summary of the invention

[0004] The purpose of the present invention is to provide a formic acid-regulated lanthanum-based metal organic framework material adsorbent and its preparation method and application. The present invention adopts formic acid to regulate the preparation of lanthanum-based metal organic framework materials, changes the small specific surface area and easy agglomeration of traditional La-MOFs materials, thereby enhancing the material's adsorption performance for phosphates; and solves the problem of low phosphate adsorption performance of existing La-MOFs materials.

[0005] To achieve the above object, the present invention first provides a method for preparing a lanthanum-based metal organic framework material adsorbent, comprising the following steps:

[0006] Lanthanum salt, terephthalic acid, formic acid and a solvent are mixed and subjected to a solvothermal reaction to obtain the lanthanum-based metal organic framework material adsorbent.

[0007] The above-mentioned preparation method specifically comprises the following steps: dissolving lanthanum salt and terephthalic acid in a solvent, then adding formic acid and mixing evenly, and performing a solvent thermal reaction to obtain the lanthanum-based metal organic framework material adsorbent.

[0008] In the above preparation method, the lanthanum salt is at least one of lanthanum nitrate and lanthanum chloride; The solvent is at least one of N,N-dimethylformamide, diethylformamide, N-methylformamide, N-methylacetamide, formamide, and N,N-dimethylpropanamide.

[0010] In the above preparation method, the molar ratio of lanthanum element in the lanthanum salt to terephthalic acid is 1:4 - 2:1; specifically, it can be 1:2.

[0011] The molar ratio of the lanthanum salt to the volume of the solvent is 0.625 - 2.5 mmol:15 - 60 mL, specifically, it can be 1.25 mmol:30 mL.

[0012] In the above preparation method, the molar ratio of lanthanum element in the lanthanum salt to formic acid is 1:9 - 72; preferably 1:18 - 72, and more preferably 1:18.

[0013] In the above preparation method, the temperature of the solvothermal reaction is 100 - 150 °C; preferably 120 - 130 °C.

[0014] The time of the solvothermal reaction is 12 - 48 h.

[0015] In the above preparation method, after the solvothermal reaction, there are steps of washing and drying the obtained solid.

[0016] Specifically, it is washed successively with DMF, deionized water, and ethanol; the drying temperature is 50 - 80 °C, specifically, it can be 60 °C.

[0017] The solvothermal reaction can be specifically carried out in a polytetrafluoroethylene reaction kettle.

[0018] The present invention also provides an adsorbent of a lanthanum-based metal-organic framework material prepared by the above preparation method.

[0019] The application of the above lanthanum-based metal-organic framework material adsorbent in removing phosphate from water also belongs to the protection scope of the present invention.

[0020] In the above application, the pH value of the water is 2 - 11, specifically, it can be 2 - 9.

[0021] The water also contains Cl - , NO 3 - , HCO 3 - , CO 3 2- and SO 4 2- at least one of them.

[0022] Finally, the present invention provides a method for removing phosphate from water, comprising the following steps: mixing the above-mentioned lanthanum-based metal-organic framework material adsorbent with phosphate-containing water.

[0023] In the above method, the concentration of the lanthanum-based metal-organic framework material adsorbent in the phosphate-containing water is 0.1-0.9 g / L.

[0024] The present invention has the following beneficial effects:

[0025] (1) Based on the traditional synthesis of La-MOFs, the present invention adds a regulator formic acid, which changes the growth direction of MOF and forms a new MOF adsorbent; the formic acid-regulated La-MOF has a larger specific surface area, more active sites for adsorbing phosphate, and better dispersibility, can quickly adsorb phosphate, and is almost not interfered by pH and coexisting ions, showing very excellent phosphate adsorption performance.

[0026] (2) The lanthanum-based metal-organic framework material adsorbent prepared by the present invention can achieve an adsorption capacity of 131.52 mgP / g for phosphate. Description of the Drawings

[0027] Figure 1 For the XRD and infrared spectra of the La 1 -TA 2 -MA x material.

[0028] Figure 2 For the SEM image of the La 1 -TA 2 -MA x material.

[0029] Figure 3 For the adsorption kinetics diagram of the La 1 -TA 2 -MA x material for phosphate.

[0030] Figure 4 For the adsorption isotherm diagram of the La 1 -TA 2 -MA x material for phosphate.

[0031] Figure 5 For the adsorption effect diagrams of the La 1 -TA 2 -MA 0 and La 1 -TA 2 -MA 18 on phosphate at different initial pH values.

[0032] Figure 6 For La 1 -TA 2 -MA 0 and La 1 -TA 2 -MA 18 Adsorption effect diagrams of phosphate under the coexistence conditions of different anions.

[0033] Figure 7 Adsorption effect diagrams of phosphate by La-MOFs synthesized under different La:MA and La:AA molar ratios.

[0034] Figure 8 For La 1 -TA 2 -MA 18 and La 1 -TA 0 -MA 20 Adsorption kinetic diagrams of phosphate by the materials. Specific implementation manners

[0035] The present invention will be further described in detail below in conjunction with specific implementation manners. The examples given are only for clarifying the present invention and not for limiting the scope of the present invention.

[0036] The experimental methods in the following examples are all conventional methods unless otherwise specified.

[0037] In the following examples, all quantitative tests are set with three repeated experiments, and the results are averaged.

[0038] The materials, reagents, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0039] Examples 1-6

[0040] A preparation method of a lanthanum-based metal-organic framework material (La 1 -TA 2 -MA x ) adsorbent is as follows:

[0041] First, weigh 0.5412 g of La(NO 3 ) 3 ·6H 2O and 0.4150g terephthalic acid (TA), measure 30mL N,N-dimethylformamide (DMF), ultrasonicate for 5 minutes to fully dissolve it, then add different amounts of formic acid in different beakers according to the molar ratio of La and formic acid (MA), ultrasonicate again for 5 minutes to fully dissolve it, and transfer it to a 100mL reactor after dissolution. Then put it in an electric blast drying oven, heat it from room temperature to 120℃, react at 120℃ for 12h, and after the reactor is cooled to room temperature, wash the obtained material with DMF, deionized water and ethanol in turn. Finally, place the material in a vacuum oven and dry it at 60℃ to obtain La. 1 -TA 2 -MA x Adsorbent.

[0042] The molar ratios of La:MA were 1:0, 1:3, 1:9, 1:18, 1:36, and 1:72, respectively, and the prepared adsorbents were named La 1 -TA 2 -MA 0 ,La 1 -TA 2 -MA 3 ,La 1 -TA 2 -MA 9 ,La 1 -TA 2 -MA 18 ,La 1 -TA 2 -MA 36 and La 1 -TA 2 -MA 72 , recorded as Example 1, Example 2, Example 3, Example 4, Example 5 and Example 6. 1 -TA 2 -MA x The adsorption capacity of the adsorbents for phosphate is shown in Table 1.

[0043] The adsorption method is as follows: potassium dihydrogen phosphate (KH 2 PO 4 ) Prepare a 50 mg P / L phosphorus solution for adsorption experiments, weigh 9 mg of the above-prepared La 1 -TA 2 -MA x The adsorbent was placed in 30 mL of phosphorus solution and then shaken in a shaker for 12 h (rotation speed 160 rpm, temperature 25° C.).

[0044] Determination of phosphate concentration: Samples were taken from the solution after the above reaction using a disposable syringe, filtered through a 0.45 μm aqueous membrane, and the phosphorus concentration in the filtrate was measured using a Hach spectrophotometer.

[0045] The experiment was set up with three replicates, and the results were averaged.

[0046] Table 1 La 1 -TA 2 -MA x Adsorption capacity of the adsorbent for phosphate

[0047] Adsorbent La:MA Phosphate adsorption capacity (mg P / g) Example 1 1:0 69.01 Example 2 1:3 69.25 Example 3 1:9 83.74 Example 4 1:18 131.52 Example 5 1:36 117.19 Example 6 1:72 104.57

[0048] Figure 1 In (a), the La 1 -TA 2 -MA x XRD patterns of the adsorbents. It can be observed from the figure that the diffraction peaks of La 1 -TA 2 -MA 0 formed without adding MA are consistent with the JCPDS card 34-1984 of lanthanum terephthalate. With the increase of the MA content, when the molar ratio of La:MA is 9, new characteristic diffraction peaks appear at positions such as 2θ = 16.37°, 23.45°, 28.87° and 33.41°, which correspond to the (110), (101), (021) and (211) crystal planes of lanthanum formate (JCPDS standard card number: 18-0674) respectively, indicating the formation of lanthanum formate at this time. With the continuous increase of the MA content, it is observed that the characteristic peaks of lanthanum terephthalate in the synthesized material completely disappear, and only the characteristic peaks of lanthanum formate exist, indicating that the increase of the MA content will promote the complete replacement of the organic ligand by MA. At the same time, it is seen that the peak shape of lanthanum formate is relatively sharp, indicating that the synthesized material has a high crystallinity.

[0049] From Figure 1 In (b), it can be seen that when the molar ratios of La:MA are 1:0, 1:3 and 1:9, the positions where the absorption peaks appear are the same. Among them, the peaks at 1400 and 1538 cm -1 correspond to the symmetric stretching and antisymmetric stretching vibration peaks of O-C=O in terephthalic acid respectively, indicating that when the MA content is low, terephthalic acid lanthanum is the main organic ligand of La 1 -TA 2 -MA x This is consistent with the XRD results. The peak at 1019 cm -1The characteristic peak is the C-O stretching vibration peak of DMF, indicating that there is still a small amount of DMF on the surface of the material. When the molar ratio of La:MA is 1:18, 1:36, and 1:72, the positions of the characteristic absorption peaks of the material are the same. Among them, the sharp peak at 1582 cm -1 is the -CH bending vibration of MA, and the peaks at 1356 and 1426 cm -1 are attributed to the =O-C-O vibration of MA. La 1 -TA 2 -MA x all have the bending vibration peak of La-O, which are located at 507, 756, and 778 cm -1 .

[0050] Figure 2 In (a)-(f) of 1 -TA 2 -MA x are the SEM images of the adsorbent. It can be seen from the figure that compared with La 1 -TA 2 -MA 18 , the materials prepared with other La:MA ratios have serious agglomeration phenomena, which will cause the active sites for adsorbing phosphate to be covered, and then lead to the deterioration of their phosphate adsorption performance.

[0051] Example 7

[0052] Study on the adsorption kinetics and adsorption isotherm of phosphorus by the La 1 -TA 2 -MA x adsorbents prepared in Examples 1-6

[0053] (1) Adsorption kinetics

[0054] Step 1: Use potassium dihydrogen phosphate (KH 2 PO 4 ) to prepare 2000 mL of phosphate solution with a concentration of 50 mg P / L. Take 1000 mL of the phosphorus solution into a 2000 mL beaker, and add La 1 -TA 2 -MA x adsorbent (the dosage is 0.3 g / L). Place the beaker on a magnetic stirrer and stir the reaction (rotation speed 240 rpm, temperature 25 °C). After a certain time, take samples, and the sampling time points are 5, 10, 15, 20, 30, 40, 50, 60, 120, 240, 360, 480, 720, 1080, 1440 min.

[0055] Step 2: The phosphorus concentration is measured in the same method as in Examples 1-6.

[0056] The experiment was set up with three replicates, and the results were averaged.

[0057] (2) Adsorption isotherm

[0058] Step 1: Prepare phosphate solutions with phosphorus concentrations of 5, 10, 25, 40, 60, 80, 100, and 200 mg P / L using potassium dihydrogen phosphate (KH 2 PO 4 ).

[0059] Step 2: Add the La 1 -TA 2 -MA x adsorbent to the above phosphorus solutions with different concentrations (dosage is 0.3 g / L), and shake in a constant temperature shaker at 25°C and 160 rpm for 12 h.

[0060] Step 3: Determine the phosphorus concentration using the same method as in Examples 1-6.

[0061] The experiment was set up with three replicates, and the results were averaged.

[0062] (3) Adsorption performance of La 1 -TA 2 -MA 0 and La 1 -TA 2 -MA 18 for phosphorus at different pH values

[0063] Step 1: Prepare a phosphate solution with a phosphorus concentration of 50 mg P / L using potassium dihydrogen phosphate (KH 2 PO 4 ), and adjust the pH of the phosphate solution with a concentration of 50 mg P / L to 2, 3, 5, 7, 9, and 11 using 0.1 mol / L HCl and NaOH solutions.

[0064] Step 2: Add the La 1 -TA 2 -MA 0 and La 1 -TA 2 -MA 18 adsorbents to the above phosphorus solutions with different pH values (dosage is 0.3 g / L), and shake in a constant temperature shaker at 25°C and 160 rpm for 12 h.

[0065] Step 3: Determine the phosphorus concentration using the same method as in Examples 1-6.

[0066] The experiment was set up with three replicates, and the results were averaged.

[0067] (4) La 1 -TA 2-MA 0 and La 1 -TA 2 -MA 18 Phosphorus adsorption performance in the presence of different anions

[0068] Step 1: Prepare a phosphate solution with a phosphorus concentration of 50 mg P / L using potassium dihydrogen phosphate (KH 2 PO 4 ). Add different types of anions Cl - , NO 3 - , HCO 3 - , CO 3 2- and SO 4 2- (the cation is K + ), and the concentration of each anion is 100 mg / L.

[0069] Step 2: Add the La 1 -TA 2 -MA 0 and La 1 -TA 2 -MA 18 adsorbents into the above phosphorus solution containing different coexisting anions (the dosage is 0.3 g / L), and shake in a constant temperature shaker at 25°C and 160 rpm for 12 h.

[0070] Step 3: Determine the phosphorus concentration in the same method as in Examples 1 - 6.

[0071] Set three replicates for the experiment, and take the average of the results.

[0072] Figure 3 and Figure 4 are the adsorption kinetics and adsorption isotherm diagrams of the La 1 -TA 2 -MA x adsorbent for phosphate. As can be seen from Figure 3 , La 1 -TA 2 -MA 0 , La 1 -TA 2 -MA 3 , La 1 -TA 2 -MA 9 and La 1 -TA 2 -MA 18 all have relatively fast adsorption rates of phosphate, showing a rapid upward trend in the first 50 min and then tending to be stable, and La1 -TA 2 -MA 18 has the largest phosphate adsorption capacity. La 1 -TA 2 -MA 36 and La 1 -TA 2 -MA 72 although have an increased phosphate adsorption capacity compared to La 1 -TA 2 -MA 3 and La 1 -TA 2 -MA 9 but their adsorption rates are significantly slowed down. The pseudo-second-order model is more suitable for the process of La 1 -TA 2 -MA x adsorbing phosphate, and the adsorption capacity calculated by the pseudo-second-order model is consistent with the experimental value, indicating that the adsorption process is mainly controlled by chemisorption.

[0073] Figure 4 The fitting results of 1 -TA 2 -MA x show that the phosphate adsorption of La 1 -TA 2 -MA 0 is more in line with the Langmuir model, indicating that the adsorption process is a uniform monolayer adsorption. The maximum adsorption capacities of La 1 -TA 2 -MA 3 ,La 1 -TA 2 -MA 9 ,La 1 -TA 2 -MA 18 ,La 1 -TA 2 -MA 36 and La 1 -TA 2 -MA 72 are 69.01, 69.25, 83.74, 131.52, 117.19 and 104.57 mg P / g, respectively.

[0074] Figure 5 For La 1 -TA 2 -MA 0 and La 1 -TA 2 -MA 18Adsorption effect diagram of phosphate. As can be seen from the figure, La 1 -TA 2 -MA 18 has better pH adaptability and lower sensitivity to pH changes than La 1 -TA 2 -MA 0 .

[0075] Figure 6 For the coexisting anions' influence on the phosphate adsorption performance of La 1 -TA 2 -MA 0 and La 1 -TA 2 -MA 18 adsorbents, the effect diagram is shown. As can be seen from the figure, the trend of La 1 -TA 2 -MA 18 adsorbing phosphate under different anion conditions is the same as that of La 1 -TA 2 -MA 0 , but the adsorption capacity of La 1 -TA 2 -MA 18 for phosphate is significantly higher than that of La 1 -TA 2 -MA 0 .

[0076] Comparative Example 1

[0077] Weigh 0.5412 g of La(NO 3 ) 3 ·6H 2 O and 0.4150 g of TA, measure 30 mL of DMF, and ultrasonicate for 5 min to dissolve them fully. Then add the regulators formic acid (MA), acetic acid (AA), and trifluoroacetic acid (TFA) into different beakers respectively, and ultrasonicate again for 5 min to dissolve them fully. After dissolution, transfer them into a 100 mL autoclave. Then put it into an electrothermal blast drying oven, heat it from room temperature to 120 °C, and react at 120 °C for 12 h. After the autoclave cools to room temperature, wash the obtained material successively with DMF, deionized water, and ethanol. Finally, place the material in a vacuum oven and dry it at a temperature of 60 °C; when the material is synthesized, it can be clearly observed by the naked eye that adding the regulators MA and AA can both obtain La-MOFs materials, while no material is formed after adding TFA.

[0078] Furthermore, the effects of La-MOFs synthesized with different monocarboxylic acid regulators on phosphate adsorption were studied. The adsorption method is as follows: the same as the adsorption method in Examples 1-6, that is, potassium dihydrogen phosphate (KH 2 PO 4 ) was used to prepare a phosphorus solution with a concentration of 50 mg P / L for the adsorption experiment. 9 mg of the above-prepared adsorbent was weighed and added to 30 mL of the phosphorus solution, and then shaken and reacted in a shaking box for 12 h (rotation speed 160 rpm, temperature 25 °C).

[0079] The determination of the phosphate concentration was the same as the method in Examples 1-6.

[0080] Figure 7 is the adsorption effect diagram of La-MOFs synthesized at different La:MA and La:AA molar ratios for phosphate. Figure 7 In (a), it is the adsorption performance diagram of La 1 -TA 2 -MA x adsorbent for phosphate. It can be seen from the figure that as the amount of MA in the La:MA molar ratio increases, the phosphate adsorption capacity of the material shows a trend of first increasing and then decreasing. Figure 7 In (b), it is the adsorption performance diagram of La 1 -TA 2 -AA x adsorbent for phosphate. It can be seen from the figure that when the La:AA molar ratio is 1:3 and 1:9, the phosphate adsorption capacity of the synthesized adsorbent hardly changes. As the content of AA further increases, the phosphate adsorption capacity of the material slightly increases. Comparatively speaking, the material synthesized by adding the regulator formic acid is more conducive to phosphate adsorption.

[0081] Comparative Example 2

[0082] Weigh 0.5412 g of La(NO 3 ) 3 ·6H 2 O and 0 g of TA, measure 30 mL of DMF, and ultrasonicate for 5 min to dissolve it completely. Then add 0.9427 mL of MA (La:MA molar ratio is 1:20) to the beaker, and ultrasonicate again for 5 min to dissolve it completely. After dissolution, transfer it to a 100 mL reaction kettle. Then place it in an electrothermal blast drying oven and heat it from room temperature to 120 °C, and react at 120 °C for 12 h. After the reaction kettle cools to room temperature, wash the obtained material with DMF, deionized water, and ethanol in sequence. Finally, place the material in a vacuum oven and dry it at a temperature of 60 °C to obtain La 1 -TA 0 -MA20 Adsorbent

[0083] Figure 8 is La 1 -TA 2- MA 18 and La 1 -TA 0 -MA 20 Adsorption kinetic graph of the adsorbent for phosphate (the adsorption kinetic test method is the same as that in Example 7). It can be seen from the graph that La 1 -TA 2- MA 18 has a much faster adsorption equilibrium time for phosphate than La 1 -TA 0 -MA 20 . At the same time, it can be observed that when the adsorption time reaches 24 h, La 1 -TA 2- MA 18 also has a higher adsorption capacity for phosphate than La 1 -TA 0 -MA 20 .

[0084] The above embodiments only exemplarily illustrate the principles and effects of the present invention, rather than being used to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a lanthanum-based metal organic framework material adsorbent, comprising the following steps: Lanthanum salt, terephthalic acid, formic acid and a solvent are mixed and subjected to a solvothermal reaction to obtain the lanthanum-based metal organic framework material adsorbent.

2. The preparation method according to claim 1, characterized in that: The lanthanum salt is at least one of lanthanum nitrate and lanthanum chloride; The solvent is at least one of N,N-dimethylformamide, diethylformamide, N-methylformamide, N-methylacetamide, formamide and N,N-dimethylpropionamide.

3. The preparation method according to claim 1 or 2, characterized in that: The molar ratio of lanthanum element to terephthalic acid in the lanthanum salt is 1:4-2:1; The volume ratio of the mole number of the lanthanum salt to the solvent is 0.625-2.5 mmol:15-60 mL.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The molar ratio of the lanthanum element to formic acid in the lanthanum salt is 1:9-72; preferably 1:18-72, and more preferably 1:

18.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The temperature of the solvent thermal reaction is 100-150°C; preferably 120-130°C; The solvent thermal reaction time is 12-48 h.

6. The lanthanum-based metal organic framework material adsorbent prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the lanthanum-based metal organic framework material adsorbent according to claim 6 in removing phosphate from water.

8. The use according to claim 7, characterized in that: The pH value of the water is 2-11; The water also contains Cl - 、NO3 - 、HCO3 - 、CO3 2- and SO4 2- At least one of .

9. A method for removing phosphate from water, comprising the following steps: mixing the lanthanum-based metal organic framework material adsorbent according to claim 6 with water containing phosphate.

10. The method according to claim 9, characterized in that: The concentration of the lanthanum-based metal organic framework material adsorbent in the phosphate-containing water is 0.1-0.9 g / L.

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